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Metal atoms observed in the thermosphere over Arecibo

Metal atoms observed in the thermosphere over Arecibo. Jonathan S. Friedman (SRI-AO) Xinzhao Chu (UCB–CIRES) Christiano Brum (SRI-AO) Steven M. Smith (BU) Jia Yue (NCAR ) (and many others). AO K Lidar – 12 March 2005. (Note the log scale). Layer descent rate is ~ 20 km/ hr , or ~ 6 m/s.

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Metal atoms observed in the thermosphere over Arecibo

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  1. Metal atoms observed in the thermosphere over Arecibo Jonathan S. Friedman (SRI-AO) Xinzhao Chu (UCB–CIRES) ChristianoBrum (SRI-AO) Steven M. Smith (BU) JiaYue (NCAR) (and many others) SA41C-03

  2. AO K Lidar – 12 March 2005 (Note the log scale) Layer descent rate is ~ 20 km/hr, or ~ 6 m/s SA41C-03

  3. Thermospheric K Chemistry Neutralization production of K • d[K]/dt = 5×10-5/s  [e-] ~ 2×104/cc and • Ionosonde echoes  [e-] ~ 2×105/cc recombination rate ≈ 10-11 cm3/s K+ lifetime is ~240 hrs in a 2×105 e-/cc Es Ionization loss of K for O2k = 5.6 × 10-9 cm3/s for NO k = 4 × 10-9cm3/s K lifetime is ~140 hrs at 135 km. K production exceeds loss by 25x SA41C-03

  4. Ionosonde measurements, 7 UT Altitude 2 4 MHz Plasma Frequency The ionogram indicates the presence of a fairly strong Es layer. 4 MHz [e-] ~ 2×105/cc SA41C-03

  5. TIL-like properties of the layer • TIL a wavefront, and a 20 km/hr (6 m/s) wave would be consistent with a semidiurnal tide or gravity wave.(Chu et al. (GRL 2011 & SA44A-03) observed periodicity in the thermosphere over McMurdo and thus were able to establish the wave parameters related to the layer.) • TIL  Periodicity in the thermosphere.Upper mesosphere? SA41C-03

  6. K Integrated Column above 110 km Statistical Noise A hint at an enhancement at 04 UT (local midnight), 6-h wave? SA41C-03

  7. Wave modulation of K densities below 100 km 10 -10 - An upward-propagating GW of period ca. 115 min is seen to reflect after 4 UT. - Discontinuity in the profile centroid at 6:40 UT. SA41C-03

  8. Thermospheric Neutral Atom Layer Summary • The characteristics of the layer are similar to those of a tidal ion layer: Phase velocity, morphology, concentration. • There is a strong Es layer prior to the appearance of the thermospheric K layer. • Neutral K production and loss rates are reasonable. • The descent rate of ~6 m/s is slower than a typical tidal ion layer (~30 m/s). Does this allow time for the neutralization? Note: Geomagnetic activity: Kp ≤ 1, low TEC. SA41C-03

  9. Conclusions • We have presented what is, to our knowledge, the first observation of a neutral metal (K) atom layer extending above 150 km into the thermosphere. • It is likely the source of the K atoms is through radiative recombination of K+ within an Es layer. • The evidence indicates the occurrence of a strong, localized sporadic E layer with sufficient K+ content over a long enough lifetime to produce detectable K through radiativerecombination, although the altitude of the Es is unknown. • After many hundreds of nights, 1000s of hours over 12 years observing this event is unique. Why? SA41C-03

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